(I don't have a lot of experience with this, so there may be errors and omissions.)

My CompTIA A+ book tells me that a laptop that truly supports ACPI will have controls for it in the BIOS. My laptop (Compaq Presario V2610US) doesn't. So ACPI functionality has to take place entirely in software.

Kanotix "Thorhammer" comes with KPowersave (as well as the "acpid" and "powersaved" daemons), but that didn't give me an option to suspend to disk or suspend to RAM. I installed "klaptopdaemon" (which shows up in the KDE Control Center as a new module, Power Control > Laptop Battery, as well as in the system tray) and went to the ACPI tab, and clicked the "Setup Helper Application" button. That put options for suspend to disk and suspend to RAM on the KPowersave menu.

(There's no need to have both KLaptopdaemon's battery monitor icon and KPowersave's battery monitor icon in the system tray, so I set KLaptopdaemon not to show its icon there.)

This laptop uses an ATI Radeon XPress 200M chipset. In order for suspend to disk to work, I had to use the "radeon" driver rather than the "fglrx" driver. I also had to pass "resume=/dev/sda6" (my swap partition) to the kernel in GRUB.

For suspend to RAM to work, I installed the uswsusp package, which is maintained by openSUSE. They have a two-part walkthrough on it (part 1, part 2). Long story short, it comes down to finding out whether your laptop is supported by the s2ram utility (mine isn't), and if not, finding the correct parameters to pass to it. After you do, you modify /etc/powersave/sleep and put in the working parameters, e.g.

SUSPEND2RAM_FORCE="yes"
SUSPEND2RAM_ACPI_SLEEP="1"

In order for suspend to RAM to work, I also had to disable the framebuffer (with "vga=0" as a kernel parameter). Makes for an ugly-looking startup.

One thing left unsolved is that I'd like the display's backlight to turn off when the screensaver ends and the screen blanks. It doesn't make sense to have a blank screen with the backlight still going. There's a utility (already installed) named radeontool that will turn on and off the backlight, but I haven't been able to make it work in conjunction with the screensaver yet. The backlight turns off for a moment, but then comes back on.